In these two plants of Nishiyama Sakata Denki, the solar panels are tilted at 40° and set at 1.8m from the ground (Fig. 6). This was for the purpose of making the snow easily slip off the panels and preventing the fallen snow from adhering to the panels. At mega solar power plants in snowy regions, solar panels are generally tilted at 30 to 40° and set at about 2m from the ground.

In Asahikawa City, there are some other solar power plants run by local enterprises. At these plants, the tilted angle and the height of the solar panels are almost the same as those at Nishiyama Sakata Denki's two plants. But on the same day when I made my inspection visit, the snow on their panels remained almost without slipping off at all (Fig. 7).

At Asahikawa Hokuto Solar Power Plant, where snow removal had been delayed, the amount of snow remaining on the panels was less than that at other enterprises' solar power plants though some snow that could not completely slip off was left on the panels.

Double-sided solar panel with top-class efficiency

Nishiyama Sakata Denki revealed it had not expected that the double-sided panel would be so effective in making snow slide off. In fact, it was the first company that ever adopted a double-sided solar panel for a mega-class solar power plant. Double-sided panels use a cell (power generating element) that generates photovoltaic power even on the reverse side.

Normal solar panels have a white plastic component called "back sheet" on the reverse side (Fig. 8). On the other hand, the adopted double-sided solar panel is covered with a transparent sheet on its reverse side so that it can absorb sunlight from both sides and generate power. Compared with normal single-sided panels, double-sided panels can generate more power because they can generate power on the reverse side.

Nishiyama Sakata Denki deployed the double-sided solar cell "EarthON" developed and manufactured by PV cell venture PVG Solutions Inc (Kohoku-ku, Yokohama City). Although the principle of double-sided solar cells has been known for quite a while, few manufacturers have commercialized the technology due to challenges such as the difficulty in boosting the conversion efficiency on the reverse side.

Having established a volume production technology that can boost conversion efficiency on the reverse side, PVG Solutions launched its double-sided solar panel product. The company manufactures the cells at its plant in Saijo City, Ehime Prefecture, and entrusts the panel assembly to manufacturers in China and Taiwan.

Nishiyama Sakata Denki decided to use the double-sided solar panel, considering such a panel that can also generate power on the reverse side to be more advantageous in snowy regions, where the reverse side of solar panels can easily receive sunshine reflected by snow on the ground.

Regarding the conversion efficiency of double-sided solar panels, there is no official figure that reflects the amount of power generation on the reverse side. It is because there is no measurement reference that assumes double-sided models in the current solar panel standards. PVG Solutions conducted verification tests for power generation using double-sided solar panels with the Kitami Institute of Technology and others in 2012.